1. Field of the Invention
The present invention relates to a module in which components are mounted on a wiring board and the components are covered with sealing resin, and also relates to a method for manufacturing the module.
2. Description of the Related Art
A module has been known, in which components are mounted on a wiring board using solder. In this type of module, a protective film, such as a solder resist which is a photosensitive resin, is disposed on a principal surface of the wiring board to protect wiring electrodes on the surface of the wiring board. At the same time, to protect the components mounted on the wiring board, the solder resist and the components are covered with sealing resin. In such a module structure, moisture penetrating into an interface between the solder resist and the sealing resin and into an interface between the solder resist and the wiring board turns to vapor when the module is mounted on an external motherboard or the like. The resulting expansion force of the vapor may create gaps in the interfaces, and this causes so-called solder splashes. That is, the solder that connects the components and the wiring board is remelted by heat produced when the module is mounted on the motherboard, flows into the gaps in the interfaces, and causes adjacent components to be short-circuited.
Japanese Unexamined Patent Application Publication No. 2005-183430 (see, e.g., paragraphs [0030] to [0040], FIG. 1) discloses a module designed to prevent solder splashes. In this module 100, as illustrated in FIG. 10, a part of a solder resist 102, the part being located on an outer region of one principal surface of a wiring board 101, is removed. Then, a component 103 mounted on the wiring board 101, the solder resist 102, and the outer region of the one principal surface of the wiring board 101 exposed by partially removing the solder resist 102 are covered by a sealing resin layer 104. The adhesion between the sealing resin layer 104 and the wiring board 101 is known to be greater than that between the solder resist 102 and the wiring board 101. When the part of the solder resist 102 on the outer region of the wiring board 101 is removed and the exposed outer region of the wiring board 101 is covered by the sealing resin layer 104, it is possible to prevent penetration of moisture from outside the module 100, and enhance the adhesion between the sealing resin layer 104 and the wiring board 101. Therefore, it is possible to prevent a creation of a gap, which may cause solder splashes, from being created in the interface between the wiring board 101 and the sealing resin layer 104.
However, even with the structure of the module 100 described above, moisture may penetrate into the interface between the wiring board 101 and the sealing resin layer 104, and this may create a gap in this interface when the module 100 is mounted on the motherboard. Then, the expansion force that is produced when the moisture turns into vapor is transmitted to the interface between the solder resist 102 and the sealing resin layer 104, and creates a gap in the interface between the solder resist 102 and the sealing resin layer 104. A difference in coefficient of linear expansion between the sealing resin layer 104 and the solder resist 102 may cause interfacial peeling and a gap between them, and may result in solder splashes.